1. Field of the Invention.
The present invention relates to a chuck for a boring tool (boring bit) for use in a percussion hand-held power tool such as a hammer drill or chisel hammer.
2. Description of the Prior Art
For an appropriate use, a tool insertable in a chuck should be secured in the chuck for joint rotation therewith and for a limited axial displacement relative thereto. To this end, the chuck is provided with radially displaceable engagement members which engage in radial recesses formed in the clamp region of the tool shank and limit the axial displacement of the tool to the axial length of the recesses. The engagement members provide for transmission of the rotational torque to the tool, engaging in the catch grooves formed in the clamp region of the tool shank. The blows are applied to the axial end surface of the tool shank and, thus, not to the chuck.
U.S. Pat. No. 5,398,946 discloses a chuck in which a ball is used as locking means. The ball formlockingly engages in an axially limited radial recess of a formlockingly received tool shank. The ball is displaceable along a chamfer radially outwardly, insuring axial displacement of the tool for releasing the tool. To provide for insertion or withdrawal of the tool, an axially displaceable outer sleeve is displaced against a preloaded force of a holding spring along the chuck. The drawback of this chuck consists in that it occupies a stable position only in its locking condition.
In the chuck disclosed in U.S. Pat. No. 5,558,478, additionally, a prismatic, radially displaceable, engagement member is radially preloaded, by a leaf spring, against a control sleeve which is displaced between its locking and release positions. The control sleeve is resiliently preloaded and is displaceable axially, together with an outer sleeve, in the direction of the power tool in which the chuck is used. Again, the drawback of this chuck consists in that it occupies a stable position only in its locking condition.
In German Publication DE 196 36 293A1, additionally, there is provided a holding member for retaining a control sleeve, which is displaced between engagement and release positions, in each of the sleeve end positions. The holding member is arranged between the control sleeve and the clamp region of the tool chuck. This holding member insures a stable position of the chuck in both its engagement, locking position and its release position. This insures an easy manual replacement of the tool with one hand. For changing the tool, the chuck is brought into its release position. In the chuck release position, the tool is changed. Upon the insertion of a new tool, the holding member releases the control sleeve that is automatically displaced in its engagement or locking position.
The object of the present invention is to provide a chuck with which a one-hand replacement of the tool is effected in a more reliable manner.
This and other objects of the present invention, which will become apparent hereinafter are achieved by providing a chuck for receiving a tool shank a clamp region of which is provided with close-ended radial recesses extending in axial direction. The chuck includes, radially displaceable engagement members formlockingly engageable in the radial recesses of the clamp region of the tool shank, and an axially displaceable control sleeve for radially displacing the engagement members between their engagement and release positions.
A resilient holding member is arranged between the control sleeve and the clamp region of the tool shank. The resilient holding member has a detent element for preventing displacement of the control sleeve into its locking position from its release position. The control sleeve is displaced into its release position upon insertion of the boring tool against a biasing force of the holding member.
Upon withdrawal of the tool, the holding member immediately releases the control sleeve, and the control sleeve springs into its locking position. Upon its insertion, the tool acts on the engagement members and through them positively displaces the control sleeve in the-direction toward its release position, without ever contacting it. Upon the complete insertion of the tool, the engagement members engage into the recesses of the clamp region of the tool shank, releasing the control sleeve, and the preloaded locking spring biases the control sleeve into its locking position in which the engagement or locking members are radially formlockingly retained in their tool locking position.
Advantageously, the control sleeve is provided with a flange portion. A portion of the control sleeve adjacent to the tool is radially coaxially surrounded by a front sleeve, and the stepped portion of the control sleeve adjacent to the power tool, which has a larger diameter, can be easily grasped by hand for displacing the sleeve axially in the direction toward the power tool.
The control sleeve has a projecting radially inward web which supports the locking spring which is preloaded in a direction toward the power tool. Such an arrangement insures an automatic displacement of the control sleeve into its locking position. The inner surface of the control sleeve forms at least partially a radial stop for the radially displaceable engagement members. At that, the engagement members advantageously radially formlockingly other portions of the chuck. The engagement members apply, with their end surfaces facing in the direction of the power tool, a positive force to the control sleeve, advantageously, to the extending radially inward web of the control sleeve.
Advantageously, the engagement members engage in oriented radially outwardly recesses formed in the extension of the control sleeve and are connected with the control sleeve with a possibility of a limited axial displacement relative thereto.
In a first embodiment of the inventive chuck, the holding member is advantageously formed as a radially resilient leaf spring and is provided with at least partially circumferentially extending connection element. The holding member is also provided with an extending radially inward contact section engageable with the clamp region of the tool shank. The detent element is provided at the outer end of the leaf spring.
The radially displaceable detent element of the holding member is formed as a bent nose at the end of an axially projecting, radially resilient portion of the leaf spring. The nose is formed with two chamfers which cooperate with two associated chamfers provided at the inner end of the control sleeve web, so that the detent element can be displaced radially upon axial displacement of the control sleeve against the biasing force of the holding member. A radially projecting portion of the holding member-forming leaf spring advantageously extends radially downwardly.
In the second embodiment of the inventive chuck, the holding member is formed as a ball surrounded by an axially and radially displaceable opening provided in the chuck. For retaining the tool in the chuck, the holding member engages the clamp region of the tool shank. The spherical cap of the holding member-forming ball forms a two-sided land which cooperates with a radially resilient sleeve-shaped spring provided with two inner chamfers. The spring is supported for an axial displacement and is connected with a control sleeve. The holding member-forming ball, upon being engaged by the spring, impedes the movement of the control sleeve to its locking position.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.